Bay window in the kitchen - implementation suggestions

I like the idea of a small en suite bathroom, we implemented it that way later on in our home back then. I think it’s better with only one door. I was also thinking about space next to the bed for a small shelf or similar, which is why I asked about the dimensions.

Unfortunately, I don't have the exact measurements yet.

I think the ~6.5m2 is also a nice size for a 'parent bathroom'.

The second door is removed and instead an open shower will be placed in the corner. There is really nothing wrong with the small bathroom, right? The bedroom doesn’t need to be very spacious – you’re only sleeping, changing, etc. there anyway. I’d rather give the children (who are still planned) a few more square meters. My wife specifically said she doesn’t need a walk-in closet or anything like that.

But these are very important BEFORE making a decision. They have to be available already, because the architect doesn’t plan without them!
Since it will be YOUR house, you MUST have the measurements and all the information, and from the very beginning!
Somehow I get the feeling that you are being too reserved towards your architect and almost don’t want to bother or upset him. That would be a really bad starting point for a house that is supposed to be yours and where open discussion is necessary.
A design without measurements is almost worthless, because even two or three smaller things could change the whole thing again. If he hasn’t communicated or provided this to you himself right away, I would take a close look to see if my expensive “dream home to live in” can be created that way.

It could also be smaller if necessary. I definitely wouldn’t see the adjacent, fairly large main bathroom of nearly 12 sqm as the only “children’s bathroom”; I can’t do much with this newly created and in my opinion overused term anyway, and often find it exaggerated in implementation. The “big” bathroom should belong to the parents, children like or in my opinion can still go to the parents’ bathroom, and when they are old enough to want to have privacy, they usually don’t want to sleep right next to mom and dad anymore, or you don’t want that the other way around. Maybe one day you will even sleep in the guest room yourself... who knows... but as an additional bathroom I basically like the en suite idea.
Additionally, I would generally at least provide a small shower in the ground floor guest/work room, because many things can/will change in the coming years. Guests and others shouldn’t have to go upstairs to shower; at some point the girlfriend/boyfriend will walk through the house or similar.
In general, you should post your entire project here and then more people who will really help you come closer to your wishes or implement them properly will respond.

Uffff......are you building a children's house? The current children's rooms are already big enough or even "too big". It is currently fashionable that children take up more space than parents (not just spatially) and determine the life of their environment, which in my opinion is not really child-friendly. I have a nuanced opinion on that. Your wife might want to have her own makeup room or you a billiard room, so the already oversized children's room does not need to be made bigger. A child can also easily go to the guest toilet on the ground floor in the morning if the parents are currently occupying the bathroom.